Beginning with its commercial introduction in the late 1940s, microwave cooking has been employed to quickly and efficiently cook various food items such as soups, frozen dinners, deserts, main dishes, side dishes, appetizers, and the like.
A microwave oven works by passing non-ionizing microwave radiation through the food to be heated. Microwave electromagnetic radiation is usually at a frequency of about 2.45 gigahertz (GHz) or, in large industrial/commercial ovens, at 915 megahertz (MHz). Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating. Polar molecules (such as water) rotate as they try to align themselves with the alternating electric field of the microwaves. Rotating molecules hit other molecules and put them into motion, thus generating heat.
The cooking chamber of a microwave oven is similar to a Faraday cage and prevents the waves from coming out of the oven. The oven door usually has a window for easy viewing, but the window has a layer of metal mesh which prevents the microwaves from exiting the oven.